one of a kind: a radio pulsing white dwarf binary star€¦introduction • white dwarfs are compact...
TRANSCRIPT
One of a kind: A radio
pulsing white dwarf binary
star
Dr. F.-J. (Josch) Hambsch
VVS, BAV, AAVSO, GEOS
Introduction
• White dwarfs are compact stars, similar in size to Earth but 200000
times more massive
• Isolated white dwarfs emit most of their power from ultraviolet to
near-infrared wavelengths,
• but when in close orbits with less dense stars, white dwarfs can strip
material from their companions,
• the resulting mass transfer can cause X-ray emission, as well as
mid-infrared radiation if the white dwarf is magnetic
• However, even in binaries, white dwarfs are rarely detected at far-
infrared or radio
• We have discovered a white dwarf / cool star binary that emits
across the electromagnetic spectrum from X-ray to radio
wavelengths
• It is the first white dwarf system observed to pulse periodically at
radio frequencies
How we found this star • Datamining by amateurs S. Hümmerich and K. Bernhard
• Comparison of ROSAT X-ray sources with photometrical
data of the Catalina Sky Survey
• Star is close to the Rho Ophiuchi nebula complex
between Sco and Oph.
• Star is correlated with the X-ray source 1RXS
J162147.0-225306
• Stable lightcurve with P = 0.1485354(4) d = 3.56 h
(Catalina data and own observations)
• Same value already known since 1971
• Amplitude change in V ~ 2 mag
AR Sco photometric variation and
radial velocity curve from CSS
Period 3.56h
ROAD: Remote Observatory
Atacama Desert
• San Pedro de Atacama
• 2450 m above sealevel
• 5000 inhabitants
• Electricity, Water, Lodging, Food, Shops
• High speed (10MB and more) internet
• + 300 clear nights / year
• Southern Hemisphere (23 deg south)
• Competent people for service
• Dark sky 22.00 mag/sq arcsec
ROAD Equipment
• 40cm f/6.8 Optimized Dall Kirkham (ODK)
• ASA DDM85 Direct Drive Mount
• FLI Atlas focuser
• FLI CFW 5-7 filter wheel
• FLI ML 16803 CCD camera (4k x 4k x 9mm)
• Win 7 PC with MAXIM, The Sky,
CCDCommander, RADMIN, Teamviewer
Weather in San Pedro (May 24, 2014)
ROAD statistics
• Setup of observatory and testing (2 weeks
July 2011)
• Start routine observations: Aug. 1, 2011
• Clear nights
– 01.08.11-31.07.12 321 nights
– 01.08.12-31.07.13 320 nights
– 01.08.13-31.07.14 335 nights
– 01.08.14-31.07.15 312 nights
– 01.08.15-31.07.16 312 nights
Observations at ROAD
• Observations during 42 nights of AR Sco
• Analysis incl. Catalina Surveys data confirmed
the period of P = 0.1485354(4) d and an
amplitude of ~2 mag (V)
• DSCT-type can therefore be rejected
• Other classification scenarios for AR Sco: – a young stellar object (YSO) based on T-Tauri type spectrum
– or a (pre-)cataclysmic variable based on period and amplitude
AR Sco phase diagram all data
P = 0.1485354(4) d
= 213.891 min
= 3.56 h
Modulation reduces
towards the red
(2 mag in V, 1.3 mag in I),
AR Sco phase diagram all data
P = 0.1485354(4) d
= 213.891 min
= 3.56 h
Modulation reduces
towards the red
(2 mag in V, 1.3 mag in I),
AR Sco Fourier transform V data
Signal at about
~2min (661 cycles/day).
AR Sco light curve during one night
Higher resolution observations
at ROAD
(10 s exposure)
Shows actually
two frequencies
Changes of about
1 mag in about 1 minute
Involvement of professional
astronomers • Contact: 27.05.2015
• First spectrum with VLT 08.06.2015
• Request for B and I filter data from ROAD
• Request for VLT X-shooter observations 19.06.2015
• ULTRACAM, SWIFT X-ray observations
• New season (Jan. 2016): VLA (radio), XMM (X-
rays), HST (ultraviolet), ULTRACAM (high-speed
photometry), and VLT spectroscopy observations
• Nature paper accepted April 26
High-speed measurements in different
wavelengths
UV
g‘
K
Radio
Frequency plot of photometry
measurements
Fundamental (beat) period ∼ 1.97 min (8.46 mHz), spin frequency nS and “beat”
frequency nB = nS − nO, where nO is the orbital frequency. Spin period is 1.95 min,
orbital period 3.56h
Spectrum with FORS* at VLT of
M companion star
FORS spectra of M star at orbital phase ~0.85 (black),
model spectra of M5 star (green)
Sum of M5 model and smooth spectrum (red)
AR Sco minus M5 model (magenta) * Focal Reducer and Low Dispersion Spectrograph
HST UV spectrum of AR Sco
ultraviolet lines
mainly come from the irradiated face of the M star
The wide band Spectral Energy
Distribution (SED) of AR Sco
Red curve: model atmpshere of M star
Blue curve: model atmopshere of WD
at assumed distance of 116 pc
The wide band Spectral Energy
Distribution (SED) of AR Sco
Blue curve: theoretical assumption
Geng et al. http://arxiv.org/pdf/1609.02508v1.pdf
Observational record
Great to see my humble telescope
amongst the big glass (VLT, WHT, HST)
Observed frequencies
nO = orbital frequency, Period = 213.891 min
nB = beat frequency, Period = 1.97 min
nS = spin frequency, Period = 1.95 min
AR Sco • AR Scorpii is definitely not a d-Scuti star.
• The stars X-ray emission is unexpected for a d-Scuti star.
• High-speed optical observations revealed pulsations so strong that
AR Sco can brighten by a factor of four within 30 sec.
• The system pulses on a 1.97 min period,
• Is the first white dwarf system observed to pulse periodically at radio
frequencies
• The pulsations reflect the spin of a magnetic white dwarf which we
find to be slowing down on a 107 yr timescale
• Although the pulsations are driven by the white dwarf’s spin, they
originate in large part from the cool star.
• AR Sco’s broad-band spectrum is characteristic of synchrotron
radiation, requiring relativistic electrons.
• These must either originate from near the white dwarf or be
generated in situ at the M star through direct interaction with the
white dwarf’s magnetosphere
Publication
• A radio pulsing white dwarf binary star • T.R. Marsh, B.T. Gänsicke, S. Hümmerich, F.-J. Hambsch, K. Bernhard,
C.Lloyd, E. Breedt, E.R. Stanway, D.T. Steeghs, S.G. Parsons, O. Toloza,
M.R. Schreiber, P.G. Jonker, J. van Roestel, T. Kupfer, A.F. Pala, V.S.
Dhillon, L.K. Hardy, S.P. Littlefair, A. Aungwerojwit, S. Arjyotha, D.
Koester, J.J. Bochinski, C.A. Haswell, P. Frank, P.J. Wheatley,
• Nature 537 (2016) 374–377 (15 September 2016)
• http://www.nature.com/nature/journal/vaop/ncurrent/full/nature18620.html
• It is not yet over, XMM satellite observations performed September 10, 11
2016
• Two theoretical papers already out
• Sure there will be more to come….
Thank you for your attention